@article {KNZ001748, title = {Shared drivers but divergent ecological responses: Insights from long-term experiments in mesic savanna grasslands}, journal = {BioScience}, volume = {66}, year = {2016}, pages = {666 - 682}, type = {Journal Articles}, abstract = {

Fire and grazing, key determinants of structure and function of savanna grasslands worldwide, have been extensively altered by humans. We used existing long-term manipulations of fire and grazing in North American and South African mesic savanna grasslands, as well as new experiments, to determine whether the impacts of fire and grazing by large herbivores differed between these systems. We found that despite a body of literature suggesting that these savanna grasslands respond uniquely to fire and grazing, their ecosystem responses (aboveground productivity) were generally similar. In contrast, plant-community responses to fire and herbivores diverged strongly between systems. The differences in plant-community responses, as well as convergence in ecosystem function, were underpinned by a common mechanism: the response of grass dominance to changing fire and grazing regimes. As a result, divergent responses of plant communities to altered fire and grazing regimes did not preclude convergence in ecosystem function.

}, keywords = {LTER-KNZ, Aboveground net primary productivity, fire, grassland, Grazing, plant community}, doi = {10.1093/biosci/biw077}, url = {https://academic.oup.com/bioscience/article/66/8/666/2464141}, author = {M.D. Smith and Alan K. Knapp and Scott. L. Collins and Burkepile, D.E. and Kirkman, K.P. and Koerner, S.E. and Thompson, D.I. and John M. Blair and Burns, C.E. and Eby, S. and Forrestel, E.J. and Fynn, R.W.S. and Govender, N. and Hagenah, N. and Hoover, D.L. and K.R. Wilcox} } @article {KNZ001588, title = {Loss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa}, journal = {Oecologia}, volume = {175}, year = {2014}, pages = {293 -303}, abstract = {

Large herbivore grazing is a widespread disturbance in mesic savanna grasslands which increases herbaceous plant community richness and diversity. However, humans are modifying the impacts of grazing on these ecosystems by removing grazers. A more general understanding of how grazer loss will impact these ecosystems is hampered by differences in the diversity of large herbivore assemblages among savanna grasslands, which can affect the way that grazing influences plant communities. To avoid this we used two unique enclosures each containing a single, functionally similar large herbivore species. Specifically, we studied a bison (Bos bison) enclosure at Konza Prairie Biological Station, USA and an African buffalo (Syncerus caffer) enclosure in Kruger National Park, South Africa. Within these enclosures we erected exclosures in annually burned and unburned sites to determine how grazer loss would impact herbaceous plant communities, while controlling for potential fire-grazing interactions. At both sites, removal of the only grazer decreased grass and forb richness, evenness and diversity, over time. However, in Kruger these changes only occurred with burning. At both sites, changes in plant communities were driven by increased dominance with herbivore exclusion. At Konza, this was caused by increased abundance of one grass species, Andropogon gerardii, while at Kruger, three grasses, Themeda triandra, Panicum coloratum, and Digitaria eriantha increased in abundance.

}, keywords = {LTER-KNZ, disturbance, fire, Grazing, Plant community richness, Species diversity}, doi = {10.1007/s00442-014-2895-9}, url = {https://link.springer.com/article/10.1007\%2Fs00442-014-2895-9}, author = {Eby, S. and Burkepile, D.E. and Fynn, R.W.S. and Burns, C.E. and Govender, N. and Hagenah, N. and Koerner, S.E. and Matchett, K.J. and Thompson, D.I. and K.R. Wilcox and Scott. L. Collins and Kirkman, K.P. and Alan K. Knapp and M.D. Smith} } @article {KNZ001590, title = {Plant community response to loss of large herbivores differs between North American and South African savanna grasslands}, journal = {Ecology}, volume = {95}, year = {2014}, pages = {808 -816}, abstract = {

Herbivory and fire shape plant community structure in grass-dominated ecosystems, but these disturbance regimes are being altered around the world. To assess the consequences of such alterations, we excluded large herbivores for seven years from mesic savanna grasslands sites burned at different frequencies in North America (Konza Prairie Biological Station, Kansas, USA) and South Africa (Kruger National Park). We hypothesized that the removal of a single grass-feeding herbivore from Konza would decrease plant community richness and shift community composition due to increased dominance by grasses. Similarly, we expected grass dominance to increase at Kruger when removing large herbivores, but because large herbivores are more diverse, targeting both grasses and forbs, at this study site, the changes due to herbivore removal would be muted. After seven years of large-herbivore exclusion, richness strongly decreased and community composition changed at Konza, whereas little change was evident at Kruger. We found that this divergence in response was largely due to differences in the traits and numbers of dominant grasses between the study sites rather than the predicted differences in herbivore assemblages. Thus, the diversity of large herbivores lost may be less important in determining plant community dynamics than the functional traits of the grasses that dominate mesic, disturbance-maintained savanna grasslands.

}, keywords = {LTER-KNZ}, doi = {10.1890/13-1828.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/13-1828.1}, author = {Koerner, S.E. and Burkepile, D.E. and Fynn, R.W.S. and Burns, C.E. and Eby, S. and Govender, N. and Hagenah, N. and Matchett, K.J. and Thompson, D.I. and K.R. Wilcox and Scott. L. Collins and Kirkman, K.P. and Alan K. Knapp and M.D. Smith} } @article {KNZ001587, title = {Responses to fire differ between South African and North American grassland communities}, journal = {Journal of Vegetation Science}, volume = {25}, year = {2014}, pages = {793 -804}, abstract = {

Question Does fire frequency affect mesic grassland plant community structure and composition similarly in North America and South Africa? Location Konza Prairie Biological Station (KNZ), Kansas, USA, and Ukulinga Research Farm (URF), KwaZulu-Natal, South Africa. Methods Plant community structure and composition were compared among annually burned, unburned and intermediate treatments within two long-term fire frequency manipulation experiments in native grasslands in North America and South Africa using comparable methodology over a 5-yr period. Because fire may reduce soil nitrogen (N) availability and thus affect plant community structure, N additions were superimposed on the fire treatments as a means of assessing direct vs indirect mechanisms driving responses to fire. Results The total number of species was higher at URF (183) than at KNZ (57). Overall divergence in plant community response to fire frequency occurred despite similar responses to nutrient additions. At KNZ, more frequent fire resulted in dominance by a few, tall, deep-rooted rhizomatous grasses (e.g. Andropogon gerardii). On unburned sites, shorter, more shade-tolerant species such as Poa pratensis increased in abundance, although A. gerardii remained dominant. Species richness increased with decreasing fire frequency at KNZ. At URF, frequent fire resulted in short, diverse grassland weakly dominated by a range of grass species, including Themeda triandra, Tristachya leucothrix and Hyparrhenia hirta. Decreasing fire frequency reduced species richness and resulted in dominance by a few, relatively tall caespitose grasses such as Aristida junciformis. There was a complete turnover of dominant species between annually burned and unburned treatments at URF, while at KNZ A. gerardii and Sorghastrum nutans occurred across the range of treatments. N addition reduced species richness in both sites. Conclusions Different responses to fire frequency between KNZ and URF are likely linked to the dominant species and their characteristic traits, including height and method of clonal reproduction, with the rhizomatous growth form of A. gerardii dominating the North American grassland. South Africa does not have an equivalent grass species; instead, a range of tufted, non-rhizomatous species dominate across the fire frequency treatments at URF. Reductions in soil N due to frequent fire did not appear to be a common mechanism driving responses in community composition in these two grasslands.

}, keywords = {LTER-KNZ, Community ecology, Divergence, Fire frequency, Konza Prairie Biological Station, Mesic grassland, nitrogen, Nutrient addition, Richness, tallgrass prairie, Ukulinga Research Farm}, doi = {10.1111/jvs.12130}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.12130}, author = {Kirkman, K. and Scott. L. Collins and M.D. Smith and Alan K. Knapp and Burkepile, D.E. and Burns, C.E. and Fynn, R.W.S. and Hagenah, N. and Koerner, S.E. and Matchett, K.J. and Thompson, D.I. and K.R. Wilcox and Wragg, P.D.} } @article {KNZ001259, title = {Controls of aboveground net primary production in mesic savanna grasslands: An inter-hemispheric comparison}, journal = {Ecosystems}, volume = {12}, year = {2009}, pages = {982 -995}, abstract = {

Patterns and controls of annual aboveground net primary productivity (ANPP) are fundamental metrics of ecosystem functioning. It is generally assumed, but rarely tested, that determinants of ANPP in one region within a biome will operate similarly throughout that biome, as long as physiognomy and climate are broadly consistent. We tested this assumption by quantifying ANPP responses to fire, grazing history, and nitrogen (N) addition in North American (NA) and South African (SA) savanna grasslands. We found that total ANPP responded in generally consistent ways to fire, grazing history, and N addition on both continents. Annual fire in both NA and SA consistently stimulated total ANPP (28\–100\%) relative to unburned treatments at sites with deep soils, and had no effect on ANPP in sites with shallow soils. Fire did not affect total ANPP in sites with a recent history of grazing, regardless of whether a single or a diverse suite of large herbivores was present. N addition interacted strongly and consistently with fire regime in both NA and SA. In annually burned sites that were not grazed, total ANPP was stimulated by N addition (29\–39\%), but there was no effect of N fertilization in the absence of fire. In contrast, responses in forb ANPP to fire and grazing were somewhat divergent across this biome. Annual fire in NA reduced forb ANPP, whereas grazing increased forb ANPP, but neither response was evident in SA. Thus, despite a consistent response in total ANPP, divergent responses in forb ANPP suggest that other aspects of community structure and ecosystem functioning differ in important ways between these mesic savanna grasslands.

}, keywords = {LTER-KNZ, ANPP, fire, Grasslands, Grazing, nitrogen, Savannas}, doi = {10.1007/s10021-009-9273-1}, url = {https://link.springer.com/article/10.1007\%2Fs10021-009-9273-1}, author = {Buis, G.M. and John M. Blair and Burkepile, D.E. and Burns, C.E. and Chamberlain, A.J. and Chapman, P. and Scott. L. Collins and Fynn, R.W.S. and Govender, N. and Kirkman, K. and M.D. Smith and Alan K. Knapp} } @article {KNZ001082, title = {Convergence and contingency in production-precipitation relationships in North American and South African C4 grasslands}, journal = {Oecologia}, volume = {149}, year = {2006}, pages = {456 -464}, abstract = {Mesic grasslands in North America and South Africa share many structural attributes, but less is known of their functional similarities. We assessed the control of a key ecosystem process, aboveground net primary production (ANPP), by interannual variation in precipitation amount and pattern via analysis of data sets (15- and 24-year periods) from long-term research programs on each continent. Both sites were dominated by C4 grasses and had similar growing season climates; thus, we expected convergence in precipitation{\textendash}ANPP relationships. Lack of convergence, however, would support an alternative hypothesis{\textemdash}that differences in evolutionary history and purportedly greater climatic variability in South Africa fundamentally alter the functioning of southern versus northern hemisphere grasslands. Neither mean annual precipitation nor mean ANPP differed between the South African and North American sites (838 vs. 857 mm/year, 423.5 vs. 461.4 g/m2 respectively) and growing season precipitation{\textendash}ANPP relationships were similar. Despite overall convergence, there were differences between sites in how the seasonal timing of precipitation affected ANPP. In particular, interannual variability in precipitation that fell during the first half of the growing season strongly affected annual ANPP in South Africa (P < 0.01), but was not related to ANPP in North America (P = 0.098). Both sites were affected similarly by late season precipitation. Divergence in the seasonal course of available soil moisture (chronically low in the winter and early spring in the South African site vs. high in the North American site) is proposed as a key contingent factor explaining differential sensitivity in ANPP to early season precipitation in these two grasslands. These long-term data sets provided no support for greater rainfall, temperature or ANPP variability in the South African versus the North American site. However, greater sensitivity of ANPP to early season precipitation in the South African grassland suggests that future patterns of productivity may be more responsive to seasonal changes in climate compared with the North American site.}, keywords = {LTER-KNZ, climate, Evolutionary history, Net primary production, Precipitation, soil moisture}, doi = {10.1007/s00442-006-0468-2}, author = {Alan K. Knapp and Burns, C.E. and Fynn, R.W.S. and Kirkman, K.P. and Morris, C.D. and M.D. Smith} }